Yeah, this has always seemed to me like a good idea, and a profit opportunity for the CAs. All the CAs get to spread FUD about each other being blacklisted, and claim that it's best practice to get two certs from different CAs (with different actual root certs, not just different resellers). Even the Let's Encrypt users will keep a fancy wildcard in their back pocket.
If you issue them from the same CSR / key, you can even configure your web server to send both certs in the certificate chain, and most clients will figure out which one they trust without requiring manual intervention by the site operator.
Doubling the cost and difficulty of CA management for a once in a... well.. we haven't yet had a major CA killed in the decades that CAs have been around.
If CAs were being killed every few months then that would be a reasonable thing to do - but not for such a rare occurrence.
